The black Smoke is fuel, can smell it and see it on the water. New TPS ordered, and reconditioned injectors installed. Idle controll valve faulty and also on order. Replaced Maf sensor already. ECT seems fine but did not check exact resistance vs temp, but it did change with temp, will also check that.

Heading out to the boat tomorrow to replace parts, will check readings voltage etc before and after.

Had the ECT available. Measured the resistance as below. Tested using steamer from my coffee machine, and the milk thermometer (dont tell SHMBO), reasonable accuracy I suppose.

The numbers seem to go in the right direction, and if the thermometer is out a little I am happy as this test shows that at opperating temp of 70degC/160F the resistance is about right at 320 which is lower than the 467 recommended. Therefore the ECM is getting the message that the engine is hot!

The black Smoke is fuel, can smell it and see it on the water. New TPS ordered, and reconditioned injectors installed. Idle controll valve faulty and also on order. Replaced Maf sensor already. ECT seems fine but did not check exact resistance vs temp, but it did change with temp, will also check that.

Heading out to the boat tomorrow to replace parts, will check readings voltage etc before and after.

Cheers

Mark

How did you determine the parts being faulty? If you tested them, fine, but if you just started replacing parts in hopes of finding the solution, it's going to be an expensive, frustrating journey. Buy a manual- it has testing procedures for the various systems, each in their own section. If you know someone who has serviced GM engines, ask them for their help.

Did you check fuel pressure, yet? What's the voltage when it's running? These need to be at the correct voltage in order to operate properly.

JimN: Read from other posts that manual is available and will order. Freight is more than book costs and 2 to 3 weeks wait.

I have heard of that mythical creature who knows how to maintain a GM V8 motor and who is not scared of it being in a boat... jokes aside yes I know a mechanic who will do it but again 2 to 3 weeks wait and expect huge $$$$. supply and demand

Rigged a tyre pressure guage to test fuel pressure, 25psi at idle but was leaking a little and I did not want too much fuel floating arround...... so I stopped.

How did you determine the parts being faulty? If you tested them, fine, but if you just started replacing parts in hopes of finding the solution, it's going to be an expensive, frustrating journey. Buy a manual- it has testing procedures for the various systems, each in their own section. If you know someone who has serviced GM engines, ask them for their help.

Did you check fuel pressure, yet? What's the voltage when it's running? These need to be at the correct voltage in order to operate properly.

JimN, thanks for your help so far! Testing parts now so trying to find fault before replacing parts. Know the idle motor is shot as it does no move with any power on or off. It stays closed permanently. The rest seem ok from the tests I have just done.

JimN: Read from other posts that manual is available and will order. Freight is more than book costs and 2 to 3 weeks wait.

I have heard of that mythical creature who knows how to maintain a GM V8 motor and who is not scared of it being in a boat... jokes aside yes I know a mechanic who will do it but again 2 to 3 weeks wait and expect huge $$$$. supply and demand

Rigged a tyre pressure guage to test fuel pressure, 25psi at idle but was leaking a little and I did not want too much fuel floating arround...... so I stopped.

How did you test the sensors? DON'T pierce the insulation on the wire. Use a stick pin and slide it into the green seal until it makes contact with the terminal, then test.

What is the idle speed of the engine? If the IAC is always closed, the RPM should be low, or it may not even idle at all. It definitely shouldn't idle well and may need the throttle to be opened just to keep it running. This may be the only real problem, although the fuel pressure is a bit low. Check the fuel filter and make sure it's clean. Your pressure should be in the 30 pound range at idle- the factory-recommended tests for fuel pressure are: Key ON/engine OFF, idle, 2000 RPM and WOT. Make notes of all test results and keep them as a baseline. Once it's running well, do all of the tests again, so you have something to compare to.

Use a fuel pressure gauge- these have a purge valve and you pcan use that to not only purge the air from the line, you can take a fuel sample (which I strongly recommend). If you know any auto mechanics, they should have one. Ply them with beer, if you have to.

Tested sensors with pin, then smeared dielectric grease over to help insulate.

Motor does idle but very lumpy, between 500rpm anf 800rpm. looking into the throttle body at idle it seems just enough air is getting through but the edges of the butterfly seem to get a fine line of white with ice and lumpy idle gets lower. One rev up and it clears the white ice ok.

WIll remove fuel filter and check, but will need a fuel pressure guage for safety.... will visit a bottle shop - for beer for mechanic!

High rev WOT still an issue with back firing / misfiring over 4100rpm. Changing to new plugs as previous plugs fouled from over fueling with faulty injectors - hope this works.

Tested sensors with pin, then smeared dielectric grease over to help insulate.

Motor does idle but very lumpy, between 500rpm anf 800rpm. looking into the throttle body at idle it seems just enough air is getting through but the edges of the butterfly seem to get a fine line of white with ice and lumpy idle gets lower. One rev up and it clears the white ice ok.

WIll remove fuel filter and check, but will need a fuel pressure guage for safety.... will visit a bottle shop - for beer for mechanic!

High rev WOT still an issue with back firing / misfiring over 4100rpm. Changing to new plugs as previous plugs fouled from over fueling with faulty injectors - hope this works.

Did someone remove all of the plug wires at one time? Verify the firing order and base timing (you need to put the ECM in 'Diagnostic Mode" for this (you can use a paper clip, inserted in terminals A and B of the diagnostic harness plug, then raise RPM to 1000).

Did someone remove all of the plug wires at one time? Verify the firing order and base timing (you need to put the ECM in 'Diagnostic Mode" for this (you can use a paper clip, inserted in terminals A and B of the diagnostic harness plug, then raise RPM to 1000).

Thanks JimN, yes we have checked the firing order and the leads are correct. We have had to adjust the timing as per my first post to dial out the pinging low down but it brings the backfire / misfire lower down the rev to 4100, advance the timing increases the pinging but backfire and misfire higher up at 4500rpm.

Then just to be difficult some times it does not do it at all......

Fresh fuel as well!

Also read on other posts this week how to set base timing and will buy a timing light and test tomorrow.

Motor still running very rich, black smoke from exhausts and black sooty plugs from an hour on the water. Also backfiring over 4000rpm!! Dream boat not so much fun anymore

This is what we have done so far:
IAC broken unit replaced with new one - working perfectly.
Injectors reconditioned, all good. Also tested with New injectors - no change. New injectors had same flow rate as old injectors ( I wonder if old injectors were swaped for bigger flow units at some time)
Fuel pressure tested with dodgy fitting onto guage. Read 25psi before leaking so I think 30psi would be a safe bet.
ECT tested as above post, all good. Reading a little high but at least telling ECM it is HOT.
TPS tested as above post, all good. Replacement part no change.
Map sensor tested as above, all good. Replacement part makes no difference.
Plugs changed & gaped at 1.3 (from factory) will adjust down to 1.1 tomorrow but should not change issue above.
Distributer cleaned.
Timing checked as per manual and 10degree BTDC @1000rpm. ( floats a little on the timing light - not rock steady but easily visible).

What the hell else is these to check - service - replace to stop it running so rich and stop the backfiring?